Overture

An overture is normally thought of as a prelude or an introductory piece of music, played before a dramatic work – ballet, opera, musical comedy, and the like.

Historically, this is generally the case, although, until the time of Gluck and Mozart the music bore no thematic relationship to the musical action that followed. Like most other types of music, the overture (or “sinfonia” in Italy) had followed the usual path of development into national styles, with French and Italian forms reaching their full pre-Gluck development under Lully and Alessandro Scarlatti respectively.

In Germany “ouvertüre” had already become a term for a suite of music that began with an overture. In the early 19th century, whilst retaining its introductory purpose (and considered most important too – Beethoven wrote four overtures to his opera, “Fidelio” before he was satisfied - the first three have come down to us as the popular “Leonora” overtures, named after the heroine of the opera) - the term began describing a single movement short descriptive piece. Felix Mendelssohn’s “Hebrides” (“Fingal’s Cave”) is considered the first of these. (Although his “Overture to A Midsummer Night’s Dream”, which is a descriptive piece written many years before the rest of the incidental music to the play, may be able to stake a claim of seniority.) The career of the “Concert Overture” as an independent piece of music had begun.

During the 19th century the overture in its original sense went through a series of transformations, becoming (as in Wagner’s “Tannhäuser”) a dramatic prelude lasting over a quarter of an hour, or a major piece for soloist, orchestra and chorus (Boito’s “Mefistofeles”) or short preludes as in Wagner’s “Lohengrin” and many of the Verdi operas, or virtually none at all (Puccini’s “La Boheme”).
The concert overture has taken various forms and reasons for being:

As a piece for an occasion – e.g.William Walton’s “Johannesburg Festival Overture” was commissioned for that city’s 70th birthday celebrations.

As a gift – Brahms wrote his “Academic Festival Overture” as a thank you for an honorary doctorate at the University of Wrocław.

As pure music – Brahms again. His “Tragic Overture” is named to describe the music therein.

As a suite – the composer could have just as easily called it a suite, but chose “overture” instead. An example is Prokofiev’s “Overture on Hebrew Themes” which is rare as it is an overture written as chamber music.

On literary themes. The most popular example would be Tchaikovsky’s “Romeo and Juliet – Fantasy Overture”; however he did the same to “Hamlet”

Descriptive of an event – Tchaikovsky’s “1812 Overture”.

Just for the heck of it – various overtures have been written just at the whim of the composer; and would have been just as acceptable (or not) as a Suite, or Romance, Serenade or any number of other available terms.